ddec iii breaking up popping misfire under different throttle pos

Are you saying backfire sound like a car does, or just like some of the cil. are not firing?

 

Check all the rocker arms and rocker shafts. You have a valve not opening

 

When is the last time you had the overhead setup.??? Detroits series 60s like to be setup more often then most engines. They suffer from valve recession into the head and they get tight.........

Your engine is telling you something..
They do need maintenance once in a while , throw it a bone. Removing the air filter is not a fix.

 

Thats a sign of a head gasket blow out between a coolant hole and 1 cil.

 

More like not closing. Its probley to late as you can burn a valve quick running it like that.

 

They will pop when not opening as well.

 

I had a small cam 350 in my W/star that burn a valve on the 1st load and it sounded like the badest camed gas hot rod on the road sitting still at truck/stop? but they put a head on it and it ran for 6 years before needing a inframe

 

I have a similar problem I have been trying to chase down for about a year now on a ddec4 series 60. Engine seems to run great, but under light load it backfires, sounds like a shotgun going off through my exhaust along with a cloud of black smoke. The truck doesn’t typically blow any smoke. I had an in frame done with a new head and injectors. This was happening before and after the inframe. Seems to happen at higher elevation. Utah Wyoming and Colorado. Usually happens somewhere near 1500 rpm when reving to downshift, or after coasting when you start putting your foot into it.